Structure and method for providing line end extensions for fin-type active regions

ABSTRACT

A semiconductor structure includes an isolation feature formed in the semiconductor substrate and a first fin-type active region. The first fin-type active region extends in a first direction. A dummy gate stack is disposed on an end region of the first fin-type active region. The dummy, gate stack may overlie an isolation structure. In an embodiment, any recess such as formed for a source/drain region in the first fin-type active region will be displaced from the isolation region by the distance the dummy gate stack overlaps the first fin-type active region.

CROSS-REFERENCE

This application is a continuation of U.S. application Ser. No.17/649,148, filed Jan. 27, 2022, which is a continuation of U.S.application Ser. No. 16/726,405, filed Dec. 24, 2019, now U.S. Pat. No.11,239,365, which is a continuation of U.S. application Ser. No.15/614,439, filed Jun. 5, 2017, now U.S. Pat. No. 10,573,751, which is adivisional of U.S. application Ser. No. 14/586,602, filed Dec. 30, 2014,now U.S. Pat. No. 9,673,328, which is a continuation-in-part of U.S.patent application Ser. No. 13/356,235 filed on Jan. 23, 2012, now U.S.Pat. No. 9,324,866, the entire disclosures of which are incorporatedherein by reference.

BACKGROUND

In advanced technologies of integrated circuit industry, strainedsemiconductor structures are used to increase the carrier mobility inthe channel and enhance circuit performance. Epitaxy growth is a stepimplemented to form the strained structure. However, the epitaxy growthis sensitive to the structure of the active regions and thecorresponding environment. In one example, faucet defects are formed andconstrain further epitaxy growth. Therefore, a structure of anintegrated circuit and a method making the same are needed to addressthe issues identified above.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isemphasized that, in accordance with the standard practice in theindustry, various features are not drawn to scale. In fact, thedimensions of the various features may be arbitrarily increased orreduced for clarity of discussion.

FIG. 1 is a top view of a semiconductor structure constructed accordingto aspects of the present disclosure in one embodiment.

FIG. 2 is a fragmental top view of the semiconductor structure of FIG. 1constructed according to aspects of the present disclosure in oneembodiment.

FIG. 3 is a sectional view of the semiconductor structure of FIG. 1along line AA′ constructed according to aspects of the presentdisclosure in one embodiment.

FIG. 4 is a flowchart of a method making the semiconductor structure ofFIG. 1 .

FIG. 5 is a flowchart of a method making a fin-like active regions inthe semiconductor structure of FIG. 1 .

FIG. 6 is a schematic diagram to illustrate patterning a hard mask forforming the fin-like active regions in the semiconductor structure ofFIG. 1 .

FIG. 7 is a sectional view of the semiconductor structure of FIG. 1along line BB′ constructed according to aspects of the presentdisclosure in one embodiment.

FIG. 8 is a fragmental top view of a semiconductor structure constructedaccording to aspects of the present disclosure in one embodiment.

FIG. 9 is a sectional view of the semiconductor structure of FIG. 8along line CC′ constructed according to aspects of the presentdisclosure in one embodiment.

FIG. 10 is a fragmental top view of a semiconductor structureconstructed according to aspects of the present disclosure in oneembodiment.

FIGS. 11A and 11B are each a sectional view of the semiconductorstructure of FIG. 8 along line DD′ constructed according to aspects ofthe present disclosure in one embodiment.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof various embodiments. Specific examples of components and arrangementsare described below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.Moreover, the formation of a first feature over or on a second featurein the description that follows may include embodiments in which thefirst and second features are formed in direct contact, and may alsoinclude embodiments in which additional features may be formedinterposing the first and second features, such that the first andsecond features may not be in direct contact.

FIG. 1 is a top view of a semiconductor structure 50 constructedaccording to aspects of the present disclosure in one embodiment. FIG. 2is a fragmental top view of the semiconductor structure 50 constructedaccording to aspects of the present disclosure in one embodiment. Thesemiconductor structure 50 and the method making the same arecollectively described with reference to FIGS. 1 and 2 .

In one embodiment, the semiconductor structure 50 is a portion of asemiconductor wafer, or particularly a portion of a semiconductor dice(or a chip). The semiconductor structure 50 includes a semiconductorsubstrate 52. In one embodiment, the semiconductor substrate includessilicon. Alternatively, the substrate 52 includes germanium or silicongermanium. In other embodiments, the substrate 52 may use anothersemiconductor material, such as diamond, silicon carbide, galliumarsenic, GaAsP, AlInAs, AlGaAs, GaInP, or other proper combinationthereof. Furthermore, the semiconductor substrate 52 may include a bulksemiconductor such as bulk silicon and an epitaxy silicon layer formedon the bulk silicon.

Referring to FIG. 1 , the semiconductor structure 50 further includesvarious active regions 54, such as active regions 54 a and 54 b. In thepresent embodiment, the active regions 54 are fin-like structuredesigned to form fin-like field effect transistors (FinFETs). In aparticular embodiment, the semiconductor structure 50 includes aplurality of fin-like active regions configured in parallel, such as afirst plurality of fin-like active regions 54 a and a second pluralityof fin-like active regions 54 b. The first plurality of fin-like activeregions 54 a and the second plurality of fin-like active regions 54 bare separated by isolation features. In one example for illustration,the first plurality of fin-like active regions 54 a are configured forn-type FinFETs (nFinFETs) and the second plurality of fin-like activeregions 54 b are configured for p-type FinFETs (pFinFETs). Variousisolation features, such as shallow trench isolation (STI) features, areformed on the semiconductor substrate 52 in a procedure to form thefin-like active regions.

The fin-like active regions 54 are formed by a proper technique. In oneexample, the formation of the fin-like active regions includes formingSTI features to define the areas for the active regions, etching thesemiconductor material (e.g., silicon) in the active regions, andepitaxy growing a semiconductor material (e.g., silicon) in the activeregions to form fin-like active regions 54. In another example, theformation of the fin-like active regions includes forming STI featuresto define the areas for the active regions, and etching to recess theSTI features such that the active regions are extruded to form fin-likeactive regions 54.

Various gate stacks are formed on the fin-like active regions 54. Thegate stacks include one or more functional gate stacks for field effecttransistors and a dummy gate stack configured over the isolationfeatures. In the present embodiment, the semiconductor structure 50includes a first gate stack 56 disposed on the first plurality offin-like active regions 54 a and a second gate stack 58 disposed on thesecond plurality of fin-like active regions 54 b. The first gate stack56 and the second gate stack 58 are configured to form respective fieldeffect transistors, such as nFinFETs and pFinFETs. Furthermore, thesemiconductor structure 50 includes a dummy gate stack 60 disposed onthe STI feature and extended to be partially over the active regions 54.Particularly, the dummy gate stack 60 is disposed on the STI featuresand covers the end portions of the active regions 54 as illustrated inFIG. 1 . State differently, the fin-like active regions 54 are extendedto the dummy gate 60 such that the end portions of fin-like activeregions 54 are underlying the dummy gate stack. In furtherance of thepresent embodiment, the first plurality of fin-like active regions 54 aare extended to the dummy gate stack 60 from one side, and the secondplurality of fin-like active regions 54 b are extended to the dummy gatestack 60 from another side such that the dummy gate stack 60 covers boththe ends of the first plurality of fin-like active regions 54 a and theends of the second plurality of fin-like active regions 54 b.

In one embodiment, each of the gate stacks 56, 58 and 60 includes a maingate 62 and a gate spacer 64 formed on the sidewalls of thecorresponding main gate 62. Each main gate of the gate stacks 56, 58 and60 includes a gate dielectric feature and a gate electrode disposed onthe gate dielectric feature. The gate dielectric feature includes one ormore dielectric material and the gate electrode includes one or moreconductive material. The gate spacer includes one or more dielectricmaterial.

Further referring to FIG. 2 , the configuration of the dummy gate stackis described with details.

FIG. 2 is a top view of the semiconductor structure 50 of FIG. 1 inportion for simplicity. In the present embodiment, the fin-like activeregions 54 are aligned in a first direction X and the gate stacks arealigned in a second direction Y perpendicular to the first direction.The dummy gate 60 includes the main gate 62 and the gate spacer 64 onthe sidewalls. The main gate 62 includes a width X defined in the firstdirection. The gate spacer 64 includes a thickness T on each sideillustrated in FIG. 2 . The first fin-like active regions 54 a have endportions embedded in (underlying) the dummy gate stack 60. Each embeddedend portion of the first fin-like active regions 54 a has a dimension ZLdefined in the first direction. FIG. 7 illustrates a cross-sectionalview of the semiconductor structure 50 of FIGS. 1 and 2 along line BB′of FIG. 2 . The first fin-like active regions 54 a are embedded in (orunderlying) spacer elements 64. The spacer elements 64 are formed on thesidewall of a dummy gate stack (e.g., dummy gate stack 60). FIG. 7depicts an end region of the first fin-line active regions 54 a.

The second fin-like active regions 54 b have end portions embedded in(underlying) the dummy gate stack 60. Each embedded end portion of thesecond fin-like active regions 54 b has a dimension ZR in the seconddirection. The first fin-like active regions 54 a and the secondfin-like active regions 54 b are spaced from each other in the firstdirection with a spacing dimension S. Various parameters defined abovesatisfies an equation as S1+ZL+ZR=X+2T. In one embodiment, thedimensions ZL and ZR of the embedded end portions of the fin-like activeregions 54 range between about 5 nm and about 10 nm. In anotherembodiment, the dummy gate stack 60 has a different width than that offunctional gate stack, such as the functional gate stack 56 or 58. Theparameters ZL and ZR define the overlaps between the fin-like activeregions (54 a or 54 b) and the dummy gate stack 60. The parameters ZLand ZR also define the offsets between the edges of the dummy gate stack60 and the edges of the isolation feature underlying the dummy gatestack 60.

FIG. 3 is a sectional view of the semiconductor structure 50 taken alonga dashed line AA′ in FIG. 1 constructed according to one embodiment ofthe present disclosure. More features are illustrated in FIG. 3 withfollowing descriptions. The semiconductor structure 50 includesfunctional gate stacks 56 and 58 and further includes a dummy gate stack60 disposed between the functional gate stacks. The dummy gate 60 isformed on the isolation feature 68 and extended in the first direction Xto the end portions of the fin-like active regions 54.

Various doped features are disposed in the semiconductor substrate 52and are formed by proper technologies, such as ion implantation. Forexample, one or more doped wells 70 are formed in the active regions. Inone embodiment, a first well 70 a is formed in the first fin-like activeregions 54 a and a second well 70 b is formed in the second fin-likeactive regions 54 b. In furtherance of the embodiment, the first well 70a includes a p-type dopant for nFinFETs and the second well 70 bincludes a n-type dopant for pFinFETs.

The semiconductor structure 50 includes one or more epitaxy grownsemiconductor features (epi features) 72 for strained effect to enhancethe circuit performance. In one embodiment, the semiconductor structure50 includes epi features 72 a and 72 b disposed on the both sides of thefirst functional gate 56. In another embodiment, the semiconductorstructure 50 includes epi features 72 c and 72 d disposed on the bothsides of the second functional gate 58. In the present embodiment, theepi features 72 a, 72 b, 72 c and 72 d are present. Particularly, theepi features 72 a and 72 b include epi grown silicon carbide with thestrain effect tuned to enhance the performance of nFinFETs formed in theactive regions 54 a and the epi features 72 c and 72 d include epi grownsilicon germanium with the strain effect tuned to enhance theperformance of pFinFETs formed in the active regions 54 b. The epifeatures are extended to the dummy gate stack 60 but are spaced awayfrom the isolation feature 68, due the offset of the dummy gate 60 tothe isolation feature 68.

The formation of the epi features includes etching the semiconductorsubstrate to form the recesses and epi growing to form the correspondingepi features, such as silicon germanium or silicon carbide. In oneembodiment, epi features 72 may be grown to extrude above the surface ofsemiconductor substrate 52.

During the etching process to form the recesses, the recesses is offsetfrom the isolation feature 68 by the dummy gate 60 such that thesidewalls of the isolation feature 68 are exposed, resulting in therecesses with surfaces of only semiconductor material (silicon in thepresent embodiment). Accordingly, the epi growth substantially occurs inthe surfaces of the recesses and the faucet defect issue is eliminated.

In the existing method, the recesses expose the surfaces of theisolation feature (STI feature). The epi growth cannot grow on thesurface of the isolation feature that is dielectric material, such assilicon oxide. Void defects are formed between the epi features and theisolation features. Those void defects are referred to as faucetdefects. In contrast, the disclosed semiconductor structure 50 and thecorresponding method eliminate the faucet defects.

The semiconductor structure 50 further includes source and drainfeatures 74 formed in the active regions 54 (e.g., 54 a and 54 b) andrespectively disposed on the sides of the corresponding functional gatestack (56 or 58). The source and drain features 74 include light dopeddrain (LDD) features substantially aligned with the corresponding maingate stack and the heavily doped source and drain (S/D) aligned with thecorresponding gate spacer 64. The LDD features and the heavily doped S/Dare collectively referred to as source and drain features 74. The sourceand drain features 74 are formed by various steps of ion implantation.In the present embodiment, the source and drain features 74 in the firstactive regions 54 a have n-type dopant, such as phosphorous, configuredto form nFinFETs. The source and drain features 74 in the second activeregions 54 b have p-type dopant, such as boron, configured to formpFinFETs.

The gate stacks (including the functional gate stacks 56 and 58 and thedummy gate stack 60) include the main gates 62 and the gate spacers 64.Each main gate stack 62 includes a gate dielectric feature 62 a and agate electrode 62 b disposed on the gate dielectric feature 62 a. Thegate dielectric features 62 a include one or more dielectric materialsdisposed on the semiconductor substrate 52. The gate electrodes 62 binclude one or more conductive materials. In one embodiment, the gatedielectric features 62 a include silicon oxide and the gate electrodes62 b include polysilicon, formed by a procedure including deposition andpatterning. The patterning includes lithography process and etchprocess.

In another embodiment, the gate dielectric features 62 a include a highk dielectric material layer and the gate electrodes 62 b include a metallayer, referred to as high k metal gates. The high k metal gates may beformed by proper procedure, such as gate-last procedure wherepolysilicon gate stacks are formed first and then replaced by etching,deposition and polishing. In this embodiment, the gate dielectricfeatures 62 a may additionally include an interfacial layer (IL)disposed between the semiconductor substrate and the high k dielectricmaterial layer. The gate electrodes 62 b may include a metal film of aproper work function to the respective transistors according to type(n-type or p-type) for tuned threshold voltage, therefore referred to aswork function metal. In this case, the work function metal for nFinFETsare different from the work function metal for pFinFETs.

In yet another embodiment, the functional gate stacks 56 and 58 includesthe high k dielectric material layer for gate dielectric and the metallayer for gate electrode but the dummy gate include silicon oxide forgate dielectric and polysilicon for gate electrode.

Referring now to FIG. 8 , a configuration of an embodiment of a dummygate stack with reference to fin-like active regions is described withdetails. In the present embodiment, the fin-like active regions 54 arealigned in a first direction X and the gate stacks are aligned in asecond direction Y perpendicular to the first direction. The dummy gate60 includes the main gate 62 and the gate spacer 64 on the sidewalls.The dummy gate 60 of FIG. 8 is illustrative of the embodiment discussedabove providing for a width of the dummy gate 60 in the horizontaldirection to be different, as illustrated greater, than the widths foractive gate structures 56 and 58. In other embodiments of the device 80,the widths of the gate structures 56, 58 and/or 60 are the same, withinfabrication tolerances.

The first fin-like active regions 54 a have end portions embedded in(underlying) the dummy gate stack 60. In particular, the end portions ofthe first fin-like active regions 54 a extend such that they areembedded under (or underlying) the main gate 62, and in particular undera gate electrode 62 b disposed on the gate dielectric feature 62 a. Eachembedded end portion of the first fin-like active regions 54 a has adimension ZA defined in the first direction. FIG. 9 illustrates across-sectional view of the semiconductor structure 80 of FIG. 8 alongline CC′ of FIG. 8 . The first fin-like active regions 54 a are embedded(underlying) the gate feature 60 including underlying the gatedielectric 62 a and the gate electrode 62 b. FIG. 9 depicts an endregion of the first fin-line active regions 54 a.

FIGS. 11A and 11B each illustrates a cross-sectional view of thesemiconductor structure 80 of FIG. 8 along line DD′ of FIG. 8 . FIGS.11A and 11B are each substantially similar to as discussed above withreference to FIG. 3 , with differences as noted herein. The device 80,including as represented in FIG. 11A/B, provides for a dummy gate 60that is formed on the isolation feature 68 and extends in the firstdirection X to overlie end portions of the fin-like active regions 54.Specifically, the spacers 64 and gate dielectric layer 62 a and gateelectrode features 62 b overlie the fin like active region 54. Theisolation feature 68 is recessed. It is noted that using chemicalmechanical polishing (CMP) processes in an embodiment, (FIG. 11B) thegate structures of devices 56, 58 and 60 have a coplanar top surface.

The second fin-like active regions 54 b have end portions underlying thedummy gate stack 60. In particular, the regions 54 b underlie the gateelectrode 62 b. Each embedded end portion of the second fin-like activeregions 54 b has a dimension ZB in the second direction. The firstfin-like active regions 54 a and the second fin-like active regions 54 bare spaced from each other in the first direction with a spacingdimension S2. Various parameters defined above satisfies an equation asS2+ZA+ZB=X2+2(T2). In one embodiment, the dimensions ZA and/or ZB of theembedded end portions of the fin-like active regions 54 range betweenabout 5 nm and about 10 nm. The dummy gate stack 60 has a differentwidth X2 than that of functional gate stack, such as the functional gatestack 56 or 58. In other embodiments, the widths are substantiallysimilar, within manufacturing process tolerances. The parameters ZA andZB define the overlap between the fin-like active regions (54 a or 54 brespectively) and the dummy gate stack 60. The parameters ZA and ZB alsodefine the offsets between the edges of the dummy gate stack 60 and theedges of the isolation feature underlying the dummy gate stack 60.

FIG. 4 is a flowchart of a method 100 forming the semiconductorstructure 50 constructed according to aspects of the present disclosureaccording to one or more embodiments. The method 100 is described withreference to FIGS. 1 through 4 .

The method 100 begins at step 102 by providing a semiconductor substrate52. The semiconductor substrate 52 includes silicon or alternativelyother suitable semiconductor material.

The method 100 proceeds to step 104 by forming fin-like active regions54. In one embodiment, the fin-like active regions 54 are formed by aprocedure including forming STI features to define the areas for theactive regions, and etching back the STI features such that the activeregions are extruded to form the fin-like active regions 54.

In furtherance of the embodiment, a more detailed procedure for theformation of the fin-like active regions 54 is provided below withreference to FIG. 5 as a flowchart of forming the fin-lie active regionsaccording to various embodiments.

At step 112, a hard mask is formed on the semiconductor substrate. Inone example, the hard mask includes a silicon oxide film (pad oxide) anda silicon nitride film on the pad oxide. The hard mask layer may beformed by a proper techniques. In one example, silicon oxide is formedby thermal oxidation and silicon nitride is formed by chemical vapordeposition (CVD).

At step 114, the hard mask layer is patterned to form various openings.The patterned hard mask layer define the areas for isolation featuresand areas for active regions. Particularly, the openings of thepatterned hard mask layer define the areas for the isolation features.The hard mask layer is patterned by lithography process and etchingprocess.

To reduce the line end shortening and corner rounding issues, twophotomasks are used to pattern the hard mask layer. The first photomaskdefines fin lines and the second photomask defines line end cut patternsand creates end-to-end spacing. As illustrated in FIG. 6 as a top viewof the hard mask layer, the first photomasks defines fin features 126and the second photomask defines line end cut patterns 128 to form thefin-like active regions 54 of the semiconductor structure 50. In oneexample, the first photomask defines the fin features aligned in a firstdirection X and the second photomask defines the line end cut feature128 aligned in a second direction Y perpendicular to the first directionX.

In one embodiment, the two photomasks are utilized in a double exposureprocedure. A photoresist layer is coated on the hard mask layer. Twoexposures are implemented sequentially with the first and secondphotomasks, respectively. Then the double exposed photoresist layer isdeveloped to form a patterned photoresist layer with openings definedtherein. An etching process follows to etch the hard mask layer throughthe openings of the patterned photoresist layer. The lithography processmay include other steps, such as soft baking post-exposure baking and/orhard baking. The etching process may include two etch steps torespectively etch silicon nitride and silicon oxide.

In another embodiment, the two photomasks are utilized in a doubleexposure and double etching procedure. A first photoresist layer ispatterned (coating, exposure and developing) using the first photomask.Then an etching process follows to etch the hard mask layer through theopenings of the first photoresist layer. Similarly, a second photoresistlayer is patterned using the second photomask. Then an etching processfollows to etch the hard mask layer through the openings of the secondphotoresist layer.

At step 116, the semiconductor substrate is etched through the openingsof the hard mask layer, forming trenches in the semiconductor trenches.The pattern of the hard mask layer is transferred to the semiconductorsubstrate.

At step 118, the trenches of the semiconductor substrate are filled withone or more dielectric materials to form shallow trench isolation (STI)features. In one embodiment, the shallow trench isolation featuresinclude silicon oxide. The silicon oxide can be filled in the trenchesby a CVD process. In various examples, the silicon oxide can be formedby a high density plasma chemical vapor deposition (HDPCVD). The siliconoxide may be alternatively formed by a high aspect ratio process (HARP).In another embodiment, the trench isolation features may include amulti-layer structure. In furtherance of the embodiment, the STIfeatures include other suitable materials, such as silicon nitride orsilicon oxynitride.

In one embodiment, a polishing process, such as chemical mechanicalpolishing (CMP), is followed to remove the excessive dielectric materialon the semiconductor substrate and planarize the surface.

At step 120, the STI features are etched back such that the STI featuresare recessed and the semiconductor portions (silicon portions) areextruded relative to the recessed STI features, resulting in fin-likeactive regions. Accordingly, the top surface of the STI features islower than the top surface of the fin-like active regions.

Referring back to FIG. 4 , after the formation of the fin-like activeregions at step 104, the method 100 proceeds to step 106 by forming gatestacks, including the functional gate stacks (56 and 58) and the dummygate stack 60. As illustrated in FIG. 3 , the gate stacks (including thefunctional gate stacks 56 and 58 and the dummy gate stack 60) includethe main gates 62 and the gate spacers 64. Each main gate stack 62includes a gate dielectric feature 62 a and a gate electrode 62 bdisposed on the gate dielectric feature 62 a. In various embodiments,the gate stacks may include polysilicon or metal for gate electrode andmay include silicon oxide and/or high k dielectric material for gatedielectric. When the gate stacks include high k dielectric and metal(referred to as high k metal gates), the formation of the high k metalgates may implement gate-first process where the high k dielectricmaterial and metal directly deposited and patterned at this step.Alternatively, high k metal gates may be formed by other techniques,such as gate-last process or high-k-last process in various embodiments.

The method 100 proceeds to step 108 by forming source and drain features74 in the active regions 54 (e.g., 54 a and 54 b). The source and drainfeatures are respectively disposed on the sides of the correspondingfunctional gate stack (56 or 58). In one embodiment, the source anddrain features 74 include light doped drain (LDD) features substantiallyaligned with the corresponding main gate stack and the heavily dopedsource and drain (S/D) aligned with the corresponding gate spacer 64.The source and drain features 74 are formed by proper technique (such asion implantation) and are followed by thermal anneal for activation. Inthe present embodiment, the source and drain features 74 in the firstactive regions 54 a include n-type dopant configured to form nFinFETs.The source and drain features 74 in the second active regions 54 binclude p-type dopant configured to form pFinFETs.

The formation of the gate stacks and the formation of the source anddrain features are integrated in one procedure. For example, the heavilydoped source and drain are formed after the formation of the gatespacer. One embodiment of the procedure to form gate stacks and thesource/drain features is described below.

The gate material layers are formed on the substrate and patterned toform gate stacks. The gate material layers include an interfacial layer(such as silicon oxide) and a high k dielectric material disposed on theinterfacial layer and a polysilicon layer on the high k dielectricmaterial layer. The patterning technique includes lithography processand etching. A hard mask may be utilized as an etch mask to pattern thegate material layers.

The LDD features are then formed by ion implantation and may be followedby thermal anneal for activation. The gate spacers are formed on thesidewalls of the gate stacks by deposition and dry etch. Particularly,the dummy gate stack 60 (including gate spacer) is formed to land on theSTI feature 68 and is extended to cover end portions of the fin-likeactive regions 54. In the present embodiment illustrated in FIGS. 1 and2 , the dummy gate 60 covers the end portions of the fin-like activeregions 54 a on one side and covers the end portions of the fin-likeactive regions 54 b on another side. In the embodiment illustrated inFIG. 10 , the ends of the fin-like active structures 54 a are embeddedunder the dummy gate stack 60.

The semiconductor substrate is then etched to form recesses. In thepresent embodiment, silicon substrate is etched using a proper etchant.The recesses are formed in the silicon substrate and are separated fromthe STI feature 68 by silicon. The offsets between the edge of the STIfeature 68 and the edge of the dummy gate stack 60 are ZL and ZR,respectively, as illustrated in FIG. 2 . The offsets ZL and ZR aredesigned to be enough such that the recesses cannot reach and expose theSTI feature 68. For example, using the examples of FIGS. 2, 8, and 10 ,the recesses are formed in the fin-like active regions 54 a between thegate features.

Then the epitaxy growth (or epi growth) is implemented to form epi grownfeatures of a semiconductor material different from the substrate toachieve proper strain effect for enhanced channel mobility. In oneembodiment, the silicon germanium is epi grown in the recesses forpFinFETs. In another embodiment, the silicon carbide is epi grown in therecesses for nFinFETs.

The epi growth may grow the epi features substantially coplanar with thesurface of the silicon surface or alternatively higher than the siliconsurface such that the epi features are extruded out. Heavily dopedsource and drain are formed by ion implantation after the epitaxygrowth.

In another embodiment, the gate spacer used for recess etching isremoved and a second gate spacer is formed on the sidewalls of the gatestack. Thus, the second gate spacer is tuned to offset the heavily dopedsource and drain while the first gate spacer is tuned to offset theoverlap of the fin end and the dummy gate stack.

In yet another embodiment, heavily doped source and drain are formedduring the epi growth wherein the epi features are in situ doped duringthe epi growth. The precursor of the ep growth includes chemical tointroduce the dopant simultaneously during the epi growth.

Other processing steps may be implemented before, during and/or afterthe method 100. In one embodiment, an interlayer dielectric (ILD) layeris formed on the substrate and the gate stack. The ILD layer isdeposited by a proper technique, such as CVD. The ILD includes adielectric material, such as silicon oxide, low k dielectric material ora combination. Then a chemical mechanical polishing (CMP) process may beapplied thereafter to polarize the surface of the ILD. In one example,the gate stack is exposed by the CMP process for the subsequentprocessing steps. In the gate-last process to form high k metal gates,the polysilicon layer is replaced by one or more metals after theformation of the ILD layer. More specifically, the polysilicon layer inthe gate stacks is removed by etching, resulting in gate trenches. Thenthe gate trenches are filled by one or more metal materials, formingmetal gate stacks. In the present embodiment, a first metal having aproper work function is deposited in the gate trenches and a secondmetal is disposed on the first metal to fill the gate trenches. Thefirst metal is also referred to as work function metal. The second metalmay include aluminum or tungsten.

In the high-k-last process, both the gate dielectric and the polysiliconare removed by etching. Afterward, the high k dielectric material andmetal are then filled in to form high k metal gate stacks.

In another example, an interconnect structure is further formed on thesubstrate and is designed to couple various transistors and otherdevices to form a functional circuit. The interconnect structureincludes various conductive features, such as metal lines for horizontalconnections and contacts/vias for vertical connections. The variousinterconnect features may implement various conductive materialsincluding copper, tungsten and silicide. In one example, a damasceneprocess is used to form copper-based multilayer interconnect structure.In another embodiment, tungsten is used to form tungsten plug in thecontact holes.

Although not shown, other features and the processing steps making thesefeatures may present, including various device features such as silicidefor contact, and multilayer interconnection (MLI). In one example, thesilicide contact layer includes nickel silicide, cobalt silicide,tungsten silicide, tantalum silicide, titanium silicide, platinumsilicide, erbium silicide, palladium silicide, or combinations thereof.The gate spacers may have a multilayer structure and may include siliconoxide, silicon nitride, silicon oxynitride, or other dielectricmaterials.

Although embodiments of the present disclosure have been described indetail, those skilled in the art should understand that they may makevarious changes, substitutions, and alterations herein without departingfrom the spirit and scope of the present disclosure. For example, thesemiconductor structure 50 includes fin-like active regions. However,the present disclosure is also applicable to a two-dimensional circuitwherein the active regions and the STI features are substantiallycoplanar. The overlap between the dummy gate stack and the end portionof the active regions, as disclosed, can be implemented to reduce thefaucet defects when the epi features are incorporated in the fieldeffect transistors for strain effect. In another example, the dummy gate60 has a width different from the functional gate stack such that theoverlap between the dummy gate and the active regions is tuned toeffectively prevent the faucet issue. In yet another example, the dummygate may include different materials, such as silicon oxide andpolysilicon while the functional gate stacks include high k dielectricmaterial and metal. In yet another embodiment, only silicon germaniumepi features are formed in the pFinFETs while the nFinFETs have sourceand drain features formed in the silicon substrate.

Thus, the present disclosure provides a semiconductor structure. Thesemiconductor structure includes a semiconductor substrate; an isolationfeature formed in the semiconductor substrate; a first active region anda second active region formed in the semiconductor substrate, whereinthe first and second active regions extend in a first direction and areseparated from each other by the isolation feature; and a dummy gatedisposed on the isolation feature, wherein the dummy gate extends in thefirst direction to the first active region from one side and to thesecond active region from another side.

In one embodiment, the semiconductor structure further includes a firstfunctional gate disposed on the first active region and configured toform a first field effect transistor; and a second functional gatedisposed on the second active region and configured to form a secondfield effect transistor.

In another embodiment, the semiconductor structure further includesfirst epitaxy features formed on the first active region and interposedby the first functional gate stack. In yet another embodiment, thesemiconductor substrate includes silicon; the first epitaxy featuresinclude silicon germanium; and the first field transistor includes oneof a p-type field effect transistor and a n-type field effecttransistor, wherein the first epitaxy features are separated from thedummy gate by a portion of the semiconductor substrate.

In another embodiment, the semiconductor structure further includessecond epitaxy features formed on the second active region andinterposed by the second functional gate stack. In yet anotherembodiment, the second epitaxy features include silicon carbide; and thesecond field transistor includes another one of the p-type field effecttransistor and n-type field effect transistor, wherein the secondepitaxy features are separated from the dummy gate by another portion ofthe semiconductor substrate.

In yet another embodiment, the first and second functional gates eachinclude a high k dielectric material layer and a metal layer on the highk dielectric material layer.

In yet another embodiment, the isolation feature is a shallow trenchisolation (STI) feature extending a first dimension S1 in the firstdirection. In another embodiment, the first active region and the secondactive region are fin-like active regions aligned in the firstdirection; and the dummy gate aligned in a second directionperpendicular to the first direction and spanning a second dimension S2in the first direction, wherein the second dimension is greater than thefirst dimension.

In yet another embodiment, the dummy gate extends to the first activeregion with a first overlap dimension Z1 in the first direction; and thedummy gate extends to the second active region with a second overlapdimension Z2 in the first direction, wherein the S1, S2, Z1 and Z2 arerelated in a formula S2=S1+Z1+Z2. In yet another embodiment, the dummygate includes a main gate stack and a gate spacer disposed on both sidesof the main gate stack; the main gate stack has a width W in the firstdirection and the gate spacer has a thickness T; and the seconddimension S2 is equal to W+2T.

The present disclosure also provides another embodiment of asemiconductor structure. The semiconductor structure includes a siliconsubstrate; first plurality of fin-like active regions formed in thesilicon substrate and oriented in a first direction; second plurality offin-like active regions formed in the silicon substrate and oriented inthe first direction; a shallow trench isolation (STI) feature formed inthe silicon substrate and interposed between the first fin-like activeregions and the second fin-like active regions; and a dummy gatedisposed on the STI feature, wherein the dummy gate extends in the firstdirection to overlap with the first fin-like active regions from oneside and to overlap with the second fin-like active regions from anotherside.

In one embodiment of the semiconductor structure, the first fin-likeactive regions each include a first end contacting the STI feature andthe second fin-like active regions each include a second end contactingthe STI feature.

In another embodiment, the STI feature spans a first dimension S1 in afirst direction; the first ends and the second ends have a firstdistance in the first direction, wherein the first distance is equal tothe first dimension S1; and the dummy gate spans a second dimension S2in the first direction, S2 being greater than S1.

In yet another embodiment, the dummy gate overlaps with the firstfin-like active regions of a first overlap dimension Z1 in the firstdirection; the dummy gate overlaps with the second fin-like activeregions of a second overlap dimension Z2 in the first direction; and S1,S2, Z1 and Z2 are related in a formula S2=S1+Z1+Z2.

In yet another embodiment, the STI feature includes a top surface lowerthan top surfaces of the first and second fin-like active regions.

The present disclosure also provides an embodiment of a method thatincludes forming an isolation feature in a semiconductor substrate;forming a first fin-like active region and a second fin-like activeregion in the semiconductor substrate and interposed by the isolationfeature; forming a dummy gate stack on the isolation feature, whereinthe dummy gate extends to the first fin-like active region from one sideand to the second fin-like active region from another side.

In one embodiment, the method further includes forming epitaxy grownsource and drain features in the first fin-like active region. Inanother embodiment, the forming of the dummy gate stack includes forminga first gate having polysilicon and replacing the polysilicon withmetal.

In yet another embodiment, the forming of the isolation feature and theforming of the first fin-like active region and the second fin-likeactive region include forming a hard mask using a first photomaskdefining an active region and a second photomask defining a cut feature,wherein the hard mask includes openings defining the first and secondfin-like active regions.

In another of the broader embodiments, provided is a semiconductorstructure. The structure includes an isolation feature formed in thesemiconductor substrate. A first fin-type active region is formed in thesemiconductor substrate. The first fin-type active region extends in afirst direction. A dummy gate stack disposed on an end region of thefirst fin-type active region.

In another of the broader embodiments, a semiconductor device includinga first plurality of fin-like active regions, an STI feature, and adummy gate is provided. The first plurality of fin-like active regionsis formed in the silicon substrate and oriented in a first direction.The shallow trench isolation (STI) feature is formed in the siliconsubstrate and interfaces with an end region of each of the firstfin-like active regions. A dummy gate is disposed on the STI feature.The dummy gate extends in the second direction to overlap with the endregion of each of the first fin-like active regions.

Also described is a method, including forming an isolation feature in asemiconductor substrate. A first fin-like active region is formed in thesemiconductor substrate and contacts the isolation feature. A dummy gatestack is formed on an end region of the isolation feature. The dummygate extends above the first fin-like active region. A functional gatestack is formed on a first region of the first fin-like active region.

The foregoing has outlined features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A semiconductor structure, comprising: asemiconductor substrate; a first fin-like active region protruding froma surface of the semiconductor substrate and extending horizontally in afirst direction, the first fin-like active region having a first endportion; a second fin-like active region protruding from the surface ofthe semiconductor substrate and extending horizontally in the firstdirection and collinear with the first fin-like active region, thesecond fin-like active region having a second end portion; a shallowtrench isolation feature disposed at a location between the firstfin-like active region and the second fin-like active region, theshallow trench isolation feature being in direct contact with the firstend portion and the second end portion; and a first functionalstructure, a second functional structure and a dummy structure, eachcomprising a main portion and two sidewall spacer elements disposed onopposite sidewalls of the respective main portions; wherein the mainportion of the first functional structure is a transistor gate electrodeof a first field-effect transistor, the first field-effect transistorfurther comprising a first source/drain feature and a secondsource/drain feature formed in the first fin-like active region atopposite sides of the first functional structure, the secondsource/drain feature being adjacent to the first end portion; andwherein the main portion of the second transistor gate electrode is atransistor gate electrode of a second field-effect transistor, thesecond field-effect transistor further comprising a third source/drainfeature and a fourth source/drain feature formed in the second fin-likeactive region at opposite sides of the second functional structure, thethird source/drain feature being adjacent to the second end portion;wherein the main portion of the dummy structure overlies the shallowtrench isolation, and the two sidewall spacer elements of the dummystructure include a first sidewall spacer element and a second sidewallspacer element, the first sidewall spacer element overlying the firstend portion, and the second sidewall spacer element overlying the secondend portion; wherein the first and the second source/drain featurescomprise epitaxial regions, and the third and the fourth source/drainfeatures comprise epitaxial regions; wherein the epitaxial regions ofthe first and second source/drain features are spaced from the shallowtrench isolation feature; wherein the first fin-like active region isone of a first plurality of fin-like active regions, and the secondfin-like active region is one of a second plurality of fin-like activeregions; wherein the first plurality of fin-like active regions areparallel to each other in a second direction perpendicular to the firstdirection, and the second plurality of fin-like active regions areparallel to each other in the second direction; wherein the shallowtrench isolation feature extends in the second direction between thefirst plurality of fin-like active regions and the second plurality offin-like active regions; wherein the first functional structure extendsover each of the first plurality of fin-like active regions; wherein thesecond functional structure extends over each of the second plurality offin-like active regions; wherein the first sidewall spacer extends overend portions of each of the first plurality of fin-like active regions;and wherein the second sidewall spacer element extends over end portionseach of the second plurality of fin-like active regions.
 2. Thesemiconductor structure of claim 1, wherein the first functionalstructure, the second functional structure, and the dummy structure areof substantially the same width in the first direction.
 3. Thesemiconductor structure of claim 1, wherein the main portion of thedummy structure is of a different material than the main portions of thefirst and the second functional structures.
 4. The semiconductorstructure of claim 3, wherein the main portions of the first and secondfunctional structures comprise a metal.
 5. The semiconductor structureof claim 4, wherein a gate dielectric of the first field-effecttransistor comprises high-k dielectric material; and wherein a gatedielectric of the second field-effect transistor comprises high-kdielectric material.
 6. The semiconductor structure of claim 4, whereinthe main portion of the dummy structure comprises polysilicon.
 7. Thesemiconductor structure of claim 1, wherein the first functionalstructure, the second functional structure, and the dummy structure areof substantially the same width in the first direction; wherein the mainportions of the first and second functional structures comprise a metal;wherein a gate dielectric of the first field-effect transistor compriseshigh-k dielectric material and a gate dielectric of the secondfield-effect transistor comprises high-k dielectric material; andwherein the main portion of the dummy structure is of a differentmaterial than the main portions of the first and the second functionalstructures.
 8. A semiconductor structure, comprising: a semiconductorsubstrate having a surface; a first transistor, comprising: first andsecond source/drain regions comprising epitaxial features of a firstfin-like active region at the surface of the semiconductor substrate andextending in a first direction, the second source/drain region adjacentto a first end portion of the first fin-like active region; and a firstgate stack disposed over a portion of the first fin-like active regionbetween the first and second source/drain regions; a second transistor,comprising: third and fourth source/drain regions comprising epitaxialfeatures of a second fin-like active region at the surface of thesemiconductor substrate, extending in the first direction and collinearwith the first fin-like active region, the third source/drain regionadjacent to a second end portion of the second fin-like active region;and a second gate stack disposed over a portion of the second fin-likeactive region between the third and fourth source/drain regions; anisolation feature disposed into the surface of the semiconductorsubstrate between the first and second fin-like active regions, whereinthe epitaxial features of the second and the third source/drain regionsare spaced from the isolation feature; and a dummy structure disposed onthe isolation feature and covering the first and second end portions ofthe first and second fin-like active regions.
 9. The semiconductorstructure of claim 8, wherein the dummy structure comprises: a firstspacer embedding the first end portion of the first fin-like activeregion; and a second spacer embedding the second end portion of thesecond fin-like active region.
 10. The semiconductor structure of claim9, wherein the dummy structure further comprises: a main portiondisposed between the first and second spacers and over the isolationfeature.
 11. The semiconductor structure of claim 8, wherein the firstfin-like active region is one of a first plurality of fin-like activeregions, and the second fin-like active region is one of a secondplurality of fin-like active regions; wherein the first plurality offin-like active regions are parallel to each other and arranged in asecond direction perpendicular to the first direction, and the secondplurality of fin-like active regions are parallel to each other andarranged in the second direction; wherein the isolation feature anddummy structure extend in the second direction between the firstplurality of fin-like active regions and the second plurality offin-like active regions.
 12. The semiconductor structure of claim 11,wherein the first gate stack extends over each of the first plurality offin-like active regions; and wherein the second gate stack extends overof the second plurality of fin-like active regions.
 13. A semiconductorstructure, comprising: a semiconductor substrate; a first fin-likeactive region at a surface of the semiconductor substrate and extendingin a first direction, the first fin-like active region having a firstend portion; a second fin-like active region at the surface of thesemiconductor substrate, extending in the first direction and collinearwith the first fin-like active region, the second fin-like active regionhaving a second end portion; an isolation feature disposed into thesurface of the substrate at a location between the first fin-like activeregion and the second fin-like active region, the isolation featurebeing in direct contact with the first end portion and the second endportion; a dummy structure comprising a first spacer element and asecond spacer element, the first spacer element overlying the first endportion and the second spacer element overlying the second end portion;a first transistor gate disposed over the first fin-like active regionbetween a first source/drain feature of the first fin-like active regionand a second source/drain feature of the first fin-like active region,the second source/drain feature being adjacent to the first end portion;a second transistor gate disposed over the second fin-like active regionbetween a third source/drain feature of the second fin-like activeregion and a fourth source/drain feature of the second fin-like activeregion, the third source/drain feature being adjacent to the second endportion; wherein the first and the second source/drain features compriseepitaxially grown regions in the first fin-like active region, and thethird and the fourth source/drain features comprise epitaxially grownregions in the second fin-like active region; and wherein the first endportion is disposed between the isolation feature and the secondsource/drain feature, and the second end portion is disposed between theisolation feature and the third source/drain feature, such that theepitaxial features of the second and the third source/drain regions arespaced from the isolation feature.
 14. The semiconductor structure ofclaim 13, wherein the first fin-like active region is one of a firstplurality of fin-like active regions, and the second fin-like activeregion is one of a second plurality of fin-like active regions; whereinthe first plurality of fin-like active regions are parallel to eachother and arranged in a second direction perpendicular to the firstdirection, and the second plurality of fin-like active regions areparallel to each other and arranged in the second direction; wherein theisolation feature extends in the second direction between the firstplurality of fin-like active regions and the second plurality offin-like active regions; wherein the first transistor gate extends inthe second direction over each of the first plurality of fin-like activeregions; and wherein the second transistor gate extends in the seconddirection over each of the second plurality of fin-like active regions.15. The semiconductor structure of claim 14, wherein the dummy structureextends in the second direction over the isolation feature.
 16. Thesemiconductor structure of claim 15, wherein the dummy structure furthercomprises: a dummy element disposed over the isolation feature andbetween the first and second spacer elements.